Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-08-08
2003-11-04
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06643105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus having a high recording density. The invention further relates to a magnetic head allowed to stably provide such a magnetic recording and reproducing apparatus as described, and more particularly relates to a magnetic head having a reproducing head with a magnetoresistive layer arranged between a pair of magnetic shield layers.
2. Related Arts
The magnetic recording and reproducing apparatus such as a magnetic disk device comprises a medium for magnetically recording information; a magnetic head provided with a recording element and a reproducing element for recording or reproducing information on the medium; a recording and reproducing operation control circuit for reproducing information on the basis of an output signal from the magnetic head and recording information on the basis of a signal input; a mechanism for rotating or moving the medium; and a positioning mechanism for deciding a position of the recording and reproducing head relative to the medium.
A recording element constituting the magnetic head comprises a coil for generating magnetic flux; a pair of magnetic cores for collecting magnetic flux; and a recording gap arranged between a pair of magnetic cores for generating a magnetic field. The magnetic cores generally used include an alloy layer of nickel and iron such as Ni
80
Fe
20
and Fe
55
Ni
45
, an alloy layer of cobalt base, or a layer having about two layers of them laminated. The thickness of each core is often set to 1 to 4 &mgr;m. The recording operation is performed by applying a magnetic field generated by conducting a recording current to the coil onto the medium.
A reproducing element constituting the magnetic head comprises a pair of magnetic shield layers, a magnetoresistive layer between the pair of magnetic shield layers and arranged spaced apart by a predetermined distance from each shield layer, and a pair of electrodes connected electrically to the magnetoresistive layer. The magnetoresistive layer can be classified roughly into an AMR layer (anisotropic magnetoresistive layer) utilizing the anisotropic magnetoresistance, and a GMR layer (giant mageto-resistive layer) utilizing the giant magnetoresistance. The AMR layer is composed of, for example, a Ni
80
Fe
20
layer having a thickness ranging from from 5 to 30 nm or the like. The GMR layer is composed of a laminate layer comprising a first ferromagnetic layer having a thickness of approximately 2 to 10 nm of which magnetization direction is changed by a magnetic field leaking from the medium, a second ferromagnetic layer having a thickness of approximately 1 to 5 nm of which the magnetization direction is almost fixed, and a non-magnetic conductive layer whose thickness is approximately 1 to 4 nm inserted between the first ferromagnetic layer and the second ferromagnetic layer. The GMR layer can obtain a higher output even by a small magnetic field compared with the AMR layer. That is, since the GMR layer is more sensitive, it is advantageous for a higher recording density of the magnetic disk device. In the magnetic disk device, a change in electro-resistance of these magnetoresistive layers is detected as an output signal by applying a detecting current. A pair of magnetic shield layers are provided for detecting a change in magnetic field leaking from the medium with high resolution. Since the narrower the spacing between the pair of shield layers, the higher resolution is obtained. Therefore the spacing between the shields is being narrowed corresponding to the future higher recording density of the magnetic recording and playback apparatus. In addition, the magnetic shield layer has a function to release, outside, heat generated in the magnetoresistive layer by applying a detecting current. As the magnetic shield layer, an Ni
80
Fe
20
layer, and an alloy layer with the former being a base are often used. Further, as the shield layer (lower shield layer) on the substrate side, sendust (Fe—Al—Si) and an alloy layer such as the amorphous of a cobalt base are sometimes used, in addition to those mentioned above. A thickness of each shield layer is generally set to 1 to 4 &mgr;m in thickness.
Where a magnetic head with the recording element and the reproducing element formed on the same substrate is used, one of the pare of magnetic cores of the recording element in the side near the reproducing element, that is, the lower core is also used as the upper shield layer of the reproducing element, in order to reduce a displaced width between a position of the write gap and a position of the masgnetoresistive layer. In case of a magnetic head in which the recording element and the reproducing element combined are unified, there is a case of employing a constitution in which for the purpose of suppressing noises during the reproducing operation, one non-magnetic layer such as alumina having a submicron thickness is inserted into the upper shield layer, and a ferromagnetic metal layer having 1 to a few &mgr;m in thickness, a non-magnetic layer having a submicron thickness, and a ferromagnetic metal layer having a thickness of 1 to a few &mgr;m are laminated sequentially.
Generally, the magnetic core of the recording element and the magnetic shield layer of the reproducing element are formed using a metal layer as a main component in any case. In this case, when the spacing of the shields is narrowed to cope with the higher density of the magnetic disk device, insulation between one or both shield layers and the magnetoreistive layer or an electrode connected to the magnetoresistive layer is often damaged due to electrostatic discharges or the like to increase a probability in which a considerable reduction in reproducing signal amplitude (the amplitude is often substantially zero) and an increase in noises occur, resulting in an erroneous operation of the magnetic disk device and the lowering of yield of the magnetic heads. The damage to the magnetic heads caused by electrostatic discharges is not limited to only the time when the magnetic heads are being fabricated. It is well known that for example, in the process in which a person comes in contact with the magnetic heads such as the work of incorporating the magnetic heads into the magnetic disk device, if the control of electrostatic discharge is not sufficient, there is the possibility of giving the damage to the magnetic heads. Further, even after the magnetic heads have been incorporated into the magnetic disk device, for example, when a charged-up person or the like comes in contact with a casing (often, an electric ground) of the magnetic disk device, a ground potential is varied to generate a potential difference in the magnetic heads, thus giving damages.
The electrostatic discharge damage to which the head is subjected can be considered roughly based on causes as follows. A first case is the case where an abnormal voltage is applied due to electrostatic discharge between a pair of electrodes connected to the magnetoresistive layer, in which case, the magnetoresistive layer is sometimes broken or fused due to heat generated by a current. A second case is the case where an abnormal voltage is applied due to electrostatic discharge between one or both of shield layers arranged with a magnetoresistive layer sandwiched and the magnetoresistive layer or an electrode(s) connected to the magnetoresistive layer, in which case, the magnetoresistive layer is sometimes broken or fused by discharge which occurs between the shield layers and the magnetoresistive layer or the electrode(s), and the shield layers and the magnetoresistive layer sometimes become short-circuited.
In any case, the magnetic head is not operated normally any longer. In particular, where the spacing of the shields is made narrower than 100 nm, the probability of giving the damage due to the discharge which occurs between the shield layers and the magnetoresistive layer or the electrodes increases rapidly. Therefore, settlement of this probl
Hoshiya Hiroyuki
Ishikawa Chiaki
Kawabe Takashi
Kimura Hisashi
Nakamoto Kazuhiro
Antonelli Terry Stout & Kraus LLP
Davis David
Hitachi , Ltd.
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